Release message

- Displays to all viewports above mobile above the global header
- Allows users to hide the message (which persists in localStorage)
- Pug ugly - needs some design love.

/cc @kungpochicken 

![gu-release-message](https://f.cloud.github.com/assets/84996/1172431/33378e8a-2121-11e3-81ff-c01beae48f17.gif)